1. Field of the Invention
The present invention is related to an optical amplifying apparatus including an optical amplifier capable of directly optically-amplifying an input signal light, and is related to a method for detecting break points within a light transmission line of the optical amplifying apparatus and an optical transmitting apparatus containing the above-described optical amplifying apparatus, and further related to a bidirectional wavelength division multiplexing optical transmitting apparatus with employment of this optical amplifying apparatus.
2. Description of the Related Art
In middle and long distance optical fiber communication systems, optical amplifiers are employed so as to amplify signal light attenuated in transmission fibers. As optical amplifiers, optical fiber amplifiers and semiconductor optical amplifiers are widely utilized. These optical amplifiers may directly amplify signal light by using rare-earth doped optical fibers as amplification media.
In any of these optical amplifiers, the light is propagated from the input side into which the signal light is inputted, to the output side from which the amplified signal light is outputted. When the light is propagated along the direction opposite to the above-described propagation direction, namely the light is entered from the output side of the optical amplifier to the input side thereof, this optical amplifier is operated under unstable conditions. In the worst case, the oscillation operation occurs, so that the optical amplifier is brought into a very unstable condition. This unstable operation may cause very serious problems in the optical transmission which should be originally carried out under stable condition by the optical amplifier. In general, such optical isolators are arranged on an input side of an optical amplifier and an output side thereof, and these optical isolators may pass the light along the above-described forward direction, but may interrupt the light propagated along the reverse direction.
To investigate a condition of an optical transmission line in an optical transmission apparatus, a loss and a break point are detected which occur in this transmission line. Normally, an optical time domain reflectometer is employed so as to test the loss and the break point of the optical transmission line. However, in an optical transmitting apparatus having plurality of optical repeaters containing optical amplifiers arranged at a half way point of the optical transmission line, the above-explained test is carried out only in such a limited optical transmission line defined from one optical repeater up to another optical repeater adjacent to the first-mentioned optical repeater in order that no optical amplifier is involved in a certain optical transmission line whose condition should be tested. Therefore, the condition test is merely and successively performed only between the adjoining optical repeaters. In other words, there is a problem that the condition test cannot be executed within a single test cycle with respect to the overall optical transmission line defined from one terminal station to the other terminal station.
When an optical amplifier is arranged in an optical transmission line, light cannot be propagated within this optical transmission line along the reverse direction. As a result, there is another problem that a bidirectional wavelength division multiplexing optical transmitting apparatus cannot be constituted in connection with the above-explained problem.